We are working on the adsorption of cationic dye with the help of a biowaste material. We observed that with increase in the temperature there is a decrease in the value of adsorption capacity (Qe). Is it possible because in most of the cases it is reported that with an increase in temperature adsorption capacity also increase in case of biowaste material.
Adsorption processes can be either endothermal or exothermal. When exothermal, you have to decrease the temperature of your material for making it more adsorbent: this is the typical case of microporous solids with gases. When endothermal, the temperature has to be changed in the opposite way, and it happens sometimes in adsorption processes in the liquid phase. When you find the opposite situation then what has been reported in the literature, it may signify that the adsorption process is different.
But artefacts may also happen. Please check before that temperature doesn't have any other effect such as precipitation or evaporation, making the solution less concentrated with therefore a lower observed adsorption.
Alain
Zeng et al., [2006]*have also found similar results when they research bisphenol-A adsorption capacity of the Xiangjiang River sediments in China. They observed that with increase in the temperature there is a decrease in the value of Bisphenol-A adsorption capacity.
*G. Zeng, C. Zhang, G. Huang, J. Yu, Q. Wang, J. Li, B. Xi, H. Liu, Adsorption behavior of bisphenol A on sediments in Xiangjiang River, Central-south China, Chemosphere, 65 (2006) 1440-1499.
Thank you Alain, I will repeat the experiment and observe the results again.
Thank you Olcayto for sharing the information of such kind of results. I will repeat the experiment and if the results again came out to be similar then this paper will really be useful for communicating my research.
The adsorption capacity of dyes may increase or decrease at higher temperatures, It all depends on the nature of the reaction and other controlling variables. If the reaction process is endothermic then adsorption may increase at higher temperature. This may be attributed to increased surface coverage at higher temperature, expansion and creation of reactive and active sites. Where the reaction is exothermic, then you may have a decrease in adsorption as at higher temperature. Therefore, you may want to double check the enthalpy and entropy values at different temperatures
Your adsorption process must be exothermic, which causes decrease of adsorption capacity with increasing temperature.
Hello Haminder,
Adsorption processes can be either endothermic or exothermic. If the the capacity of adsorption (Qo) of an entity increases with increase in temperature, then the process is endothermic, and if it decreases with increase in temperature, then it is exothermic. By performing the experiment at different temperatures and plotting Kd versus 1/T (T in Kelvin) one can obtain thermodynamic data such as delta H, delta G and delta S. If delta H is positive and decreases with increase in temperature , then the adsorption process is endothermic, and if it increases with increase in temperature, then it is exothermic. Further more if delta G decreases with increase in themperature it indicated an endothermic process, while if it increases with increase in temperature , it indicates an exothermic process. i hope this helps
Start with delta G = delta H - T delta S.
In true adsorption, entropy decreases because the adsorbent is constrained to two dimensions rather than three - in other words, it is a more ordered situation and delta S is
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